(1)1/3
(2)甲知道乙每局不出什么,所以每局甲获胜和战平概率均为0.5
P(x=3)=(0.5)^3=0.125
P(x=4)=C(3,1)*(0.5)^4=0.1875
P(x=5)=1-0.125-0.1875=0.6875
E(x)=3*0.125+4*0.1875+5*0.6875=4.5625
(1)1/3
(2)甲知道乙每局不出什么,所以每局甲获胜和战平概率均为0.5
P(x=3)=(0.5)^3=0.125
P(x=4)=C(3,1)*(0.5)^4=0.1875
P(x=5)=1-0.125-0.1875=0.6875
E(x)=3*0.125+4*0.1875+5*0.6875=4.5625